1. Field of the Invention
The present invention relates generally to a built-in antenna module embedded in a portable wireless terminal, and in particular, to a built-in antenna module for a portable wireless terminal configured to improve a radiation characteristic of a Planar Inverted-F Antenna (PIFA), and antenna performance such as reducing the Specific Absorption Rate (SAR).
2. Description of the Related Art
Recently, terminals with various functions and designs are being introduced. Consumers' demands for smaller, lighter and slimmer terminals with various functions are increasing. To meet such consumers' demands, terminal providers are focusing on reducing the volume of a terminal while maintaining or improving functions thereof.
In regard to an antenna, a rod antenna (or a whip antenna) and a helical antenna that protrude outwardly of a terminal are susceptible to drop damage, and reduce portability of the terminal. Therefore, a plate type built-in antenna (i.e., a so called ‘internal antenna’ or ‘intenna’) installed inside a terminal is widely used, and various efforts have been made to improve a characteristic of the built-in antenna and also improve productivity and assembly thereof.
In general, the built-in antenna module includes a predetermined plate-type antenna radiator that is electrically connected onto a main board (i.e., Radio Frequency board) of a terminal. The built-in antenna radiator has two feed lines. One of the feed lines is electrically connected to an antenna feed unit of the main board, and the other one is operated, grounded to a ground layer formed as a conductor of the main board having a multi-layered structure. Here, the ground layer is formed or installed at the farthest location of the main board from the antenna radiator. The antenna radiator has a predetermined distance from the ground layer. The antenna radiator is grounded with only a ground point and a feed point extending downward, separated from the main body at the predetermined distance by a predetermined antenna carrier. Here, the antenna carrier is formed to facilitate fixation to the main board.
The plate type built-in antenna radiator having such feed and ground structures is called a Planar Inverted F-Antenna (PIFA) radiator. The PIFA has been known to improve antenna performance as the size of a radiator, an area of a ground surface, and a distance between the radiator and the ground surface increase.
To meet such conditions for improving the PIFA characteristics while minimizing the volume of a terminal, a separate ground plate with a predetermined distance is used on a surface of a main board opposite to a surface where the antenna radiator is installed, so that the distance between the antenna radiator and the ground surface can be increased as much as possible and thus the radiation characteristic can be improved.
However, the structure requires a complicated assembly process and a high terminal manufacturing cost because of the installation of the separate ground plate, and has limitations in expanding the distance between the antenna radiator and the ground surface using the ground plate.